Variable-frequency generator.



G. FAGGIOLI.

VARIABLE FREQUENCY GENERATOR.

APPLICATION FILED MAY 7, 1908.

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GIUSEPPE FACCIOLI, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERALELECTRIC COMPANY, A CORFORATION OF NEW YORK.

VARIABLE-FREQUENCY GENERATOR.

To all whom it may concern:

Be it known that I, Gitisnrrn FACCIOLI, a subject of the King of Italy,residing at Schenectady, county of Schenectady, State of New York, haveinvented certain new and useful Improvements in Valiable-FrequencyGenerators, of which the following is a specification.

My invention relates to alternating-current generators, and its objectis to provide a self-exciting alternating-current generator capable ofdelivering current at frequencies which may be varied over a wide range.Such a generator finds a useful application in supplying current toinduction motors for driving cars, locomotives, or other mechanism whichare to be driven at variable speeds.

A self-exciting alternating-currentgenerator has been proposedheretofore, in a Patent- No. 933,399, issued to lVilli-am Stanley,September 7, 1909, said machine comprising stator and rotor windings,the latter provided with a commutator, and the two windings connected toeach other and to the load-circuit. Such a machine is self-exciting, theexciting-current flowing through stator and rotor windings in series,and the load-current flowing from both stator and rotor windings to theload-circuit. Furthermore, the frequency of such a machine does notdepend entirely upon the number of poles and the speed of rotation, butdepends also on the ratio of stator to rotor turns, and is equal to thefrequency of rotation (that is, the number of pairs of poles times therevolutions per second) multiplied by the number of rotor turns anddivided by the sum of the stator and rotor turns. Thus, if stator androtor have the same number of turns, the frequency of the currentdelivered is one-half the frequency of rotation.

My invent-ion consists in adapting a machine of this type for deliveringcurrents, the frequency of which may be varied over wide ranges. Iaccomplish this by connecting the stator and rotor windings to eachother through a variable voltage transformer, instead of directly. WViththe connection thus made, the frequency of the currents delivered isequal to the frequency of rotation multiplied by the secondary turns ofthe transformer, and divided by the sum of the secondary and primaryturns of the transformer; those transformer turns which Specification ofLetters Patent.

Application filed May 7, 1908.

Patented Feb. 15, 1910.

Serial No. 421,358.

are connected to the rotor terminals'being called, for convenience. theprimary turns, and those connected to the stator terminals being calledthe secondary turns. By varying the ratio of transformation of thetransformer, the ratio of the secondary turns to the sum of thesecondary and primary turns is varied, and consequently the frequency ofthe currents generated in the machine may be varied over wide ranges.

My invention will best be understood by reference to the accompanyingdrawings, in which Figure 1 shows diagrammatically a variable frequencyself exciting alternatingcurrentgenerator arranged in accordance with myinvention, and Figs. 2 to t are modifications of the same.

In Fig. 1, A represents the stator winding, and B the rotor winding,which latter is provided with a commutator and two sets of commutatorbrushes 5 Z) and b b. The arrangement of brushes indicated is that for abipolar two-phase generator. The stator winding is provided with twosets of terminals, a. a and a (1 corresponding in position to the twosets of rotor brushes. The rotor brushes 6 7) and the stator terminals(4. a are connected together through a variable-ratio transformer C. Thestator and rotor terminals for the other phases are similarly connectedthrough a variable-ratio transformer C. The lines D D represent onephase of the load-circuit, and the lines D D, the other phase.

A machine arranged as shown in Fig. 1 has a revolving field, the speedof which determines the frequency generated in the machine, and also theratio of the voltages induced by it in the rotor and stator,respectively. Consequently, a given generated frequency corresponds to acertain ratio of induced voltage in stator and rotor. Now, since theratio of the terminal-voltages of stator and rotor can be varied byvarying the ratio of transformation of the transformers C and C, itfollows that this variation of the ratio of transformation varies thefrequency'of the currents generated in the machine. For instance,suppose the raratio of the transformer turns connected to the rotor tothe number of transformer turns connected to the stator is decreased;this means that the terminal-voltage of the rotor is decreased withrespect to the stator, and,

therefore, the speed at which the field-flux revolves must increase, soas to cut the stator turns faster, and the rotor turns at a lower rate.In other words, the frequency of the machine is increased.

In place of a transformer having two distinct windings, a single-windingtransformer, or auto-transformer, may be employed. Furthermore, thefrequency may be controlled by varying the number of transformer turnsconnected to the stator of the machine, instead of those connected tothe rotor. Such an arrangement is shown in Fig. 2, in which thetransformer G has a single winding, and in which the number oftransformer-turns connected to the stator winding are varied. In Fig. 2,the connections of the other phase are omitted, for the sake ofsimplicity, since they are identical with those shown for the firstphase. An other difierence between Figs. 1 and 2 is the points at whichthe load-circuit D D is connected to the machine. In Fig. 1, theload-circuit is connected to the transformer leads connected to thestator winding, while in Fig. 2 the load-circuit is connected to thetransformer-leads connected to the rotor. This change affects theregulation of the machine. The arrangement of Fig. 1 gives poorerregulation at low power-factor than the arrangement of Fig. 2.

Instead of connecting the load-circuit to either winding of thegenerator directly, it may be connected to the machine inductively, asshown in Fig. 3. In this figure, the trans former C has a secondarywinding to which the load-circuit is connected, in addition to the twowindings shown in Fig. 1. Thus the frequency-regulating transformer mayhave either one, two or three windings.

By properly connecting the load-circuit, it is possible to compound themachine, so as to give a constant voltage, or rising voltage, withincrease of load. Such an arrangement is shown in Fig. 4, in which theload-circuit D D; is connected to points a on the stator winding inadvance of the points a to which the secondary winding of transformer Ois connected; the direction of rotation of the rotor being indicated bythe arrow. With this arrangement the current flowing from the rotor tothe load-circuit flows through a portion of the stator winding andproduces a compounding effect. The amount of compounding depends uponthe displacement between the stator terminals a and a.

Many other connections of the machine wmdmgs, the variable-ratiotransformer,

and the 1oad-circuit will be obvious to those skilled in the art.Furthermore, auxiliary regulating devices may be employed in combinationwith the variable-ratio transformer, if desired. Accordingly, I do notdesire to limit myself to the particular connections shown, but aim inthe appended claims to cover all modifications which are within thescope of my invention.

lVhat I claim as new and desire to secure by Letters Patent of theUnited States, is:

1; A variablefrequency self-exciting alternating-current generator,having stator and rotor windings, one of said windings being providedwith a commutator and brushes, said windings being connected to eachother and to the load-circuit, and a variable-ratio transformer includedin the connections between said windings.

2. A varlable-frequency self-exciting alternating-current generator,having stator and rotor windings, one of said windings being providedwith a commutator and brushes, a variable-ratio transformer throughwhich said windings are connected to each other, and a load-circuitsupplied with current from said generator.

8. A variable-frequency self-exciting alternatin -current generatorhaving stator and rotor windings, one of said windings leing' providedwith a commutator and brushes, a transformer having primary andsecondary leads connected to the rotor and stator windings respectively,means for varying the ratio of transformation of said transformer, and aload-circuit supplied with current from said generator.

4. A variable-frequency self-exciting alternating current generatorhaving stator and rotor windings, one of said windings being providedwith a commutator and 1 brushes, a transformer having primary andsecondary leads connected to the rotor and stator windings respectively,means for varying the ratio of transformation of said transformer, and aload-circuit connected Witnesses v BENJAMIN B. HULL, HELEN ORroRD.

